The present invention relates generally to liquid crystal displays, and more particularly, to a method of attaching optical components and optical component assemblies to a liquid crystal display while controlling adhesive bondline thicknesses between the optical components and the liquid crystal display.
Liquid crystal displays (LCDs) include a liquid crystal material sandwiched between two sheets of glass. The two sheets of glass are typically a substrate and a color filter. Frequently, it is desirable to alter or enhance the performance of the LCD by attaching additional optical components to one or both of the LCD""s two sheets of glass. These additional optical components can be items such as glass plates, diffusers, rigid compensators, heaters, and flexible films such as polarizers, retarders and dry film adhesives. Also, two or more of these optical components can be pre-assembled into an optical component assembly which is subsequently attached to the LCD. By way of example, organic films can be sandwiched between glass plates and bonded to the LCD glass in order to optically compensate the LCD.
Attaching additional optical components or optical component assemblies to an LCD presents a number of significant problems. First, the choice of adhesive used is critical to the display""s performance. For instance, the index of refraction of the adhesive should closely match that of the optical components. Also, the adhesive should be as transparent as possible. These limitations and others will render many adhesives undesirable choices.
A second problem is related to the sensitivity of LCDs to strain. Strain on an LCD can cause performance defects such as Newton rings. High durometer (hard) adhesives, such as epoxy, used to attach optical components to an LCD typically cause strain on the LCD, and thus cause strain related defects as well. A related problem is due to the expensive nature and reparability of large LCDs. With some adhesives, once laminated (i.e., once the optical components or assemblies have been attached to the LCD), the LCD may be considered unrepairable. This is largely due to the strength of the bond, between the LCD glass and the glass of the optical component, resulting from the adhesive.
Some manufacturers of LCDs have, as a result of the problems associated with the use of available adhesives and known assembly methods, turned away from the adhesive approach to attaching optical components to the LCD. Instead, they mechanically attach the component to the LCD such that an air gap is formed between the two, thereby reducing strain and possibly improving reparability. However, this method is undesirable because it adversely effects the reflectance and contrast of the display.
Solutions to many of the above-mentioned problems are disclosed in commonly owned U.S. Pat. No. 5,867,241, issued on Feb. 2, 1999 to Sampica et al., and entitled xe2x80x9cLIQUID CRYSTAL DISPLAY LAMINATION WITH SILICONE GEL ADHESIVExe2x80x9d, which is herein incorporated by reference in its entirety. This patent teaches methods of bonding organic films or other optical components, which are sandwiched between glass, to the LCD with a silicone gel. Even with the use of silicone gel adhesive as taught in the above-referenced patent, a uniform bondline (gel joint) is necessary to enable disassembly and repair of the laminated stack and to optimize optical performance. It has been found that using some fabrication techniques, capillary action of the silicone gel between platens of the lamination fixture and the glass of the optical components or of the LCD can cause the cured bondlines to vary by a ratio of as much as 5 to 1. This undesirable effect renders it difficult to disassemble the laminated stack because the bondline can be too thin in the middle to pass a blade or wire without damaging the LCD. Another side effect of this non-uniform bondline is difficulty in achieving an adequate seal on the front surface.
A liquid crystal display optical component stackup is created with reduced defects typically caused by adhesive materials used to attach optical components to the liquid crystal display, and with improved bond line control. First and second optical components are placed in a fixture having a plurality of pins extending from a platen. A layer of silicone gel is placed between the first and second optical components. The plurality of pins orient the first and second optical components to achieve a desired alignment. A plurality of standoffs extending from the platen maintain the first optical component a distance above the first platen. This eliminates the possibility of capillary action occurring between the platen and the first optical component due to the silicone gel adhesive, thereby aiding in bond line control.